1. Field of the invention
The invention relates to an apparatus for expanding comminuted tobacco material.
The term "comminuted tobacco material" includes in particular cut rib and/or leaf material and reconstituted tobacco.
2. Description of the prior art
German Pat. No. 3,147,846 discloses an expansion method in which the tobacco material is subjected in a moist state within an extremely short period of time to a great temperature increase with pressure reaction. The resulting abrupt evaporation of the liquid contained in the tobacco particles, i.e. water, leads to an improvement of the filling power of the tobacco material by 30 to 100% without producing any appreciable destruction of the structure of the tobacco cells. In spite of the pronounced expansion and thus improvement in the filling power, the structure of the tobacco particles obtained immediately after the expansion is retained even in the further processing of the tobacco material.
A further apparatus for expanding comminuted tobacco material is shown in FIG. 5 in German Pat. No. 3,147,846 and comprises a rotary vane feeder for the supply of the tobacco material to an expansion chamber, a nozzle opening in a wall of the expansion chamber for introducing a hot gas for accelerating the tobacco material under pressure drop to at least 50 m/s with a residence time of the tobacce material in the expansion chamber of less than about 1/10 s and a delay tube following the expansion chamber.
The tobacco material entering the expansion system via the rotary, vane feeder impinges substantially perpendicularly on the free jet steam emerging from the nozzle opening, is accelerated by said free jet and at the same time expanded, and is carried away substantially horizontally to a drying means. When the tobacco material enters the expansion chamber, the steam condenses abruptly on the tobacco particles and within fractions of a second effects an increase of moisture and temperature up to the proximity of the condensation temperature corresponding to the pressure in the expansion chamber. Thereafter the tobacco particles are sucked into the reduced pressure in the free jet. The high heat and material exchange and the low pressure in the free jet lead to a "flash evaporation" of portions of the water disposed in the tobacco and thus effect the expansion of the tobacco particles.
For drying the resulting steam/tobacco-material mixture is blown directly into an air stream dryer.
In practice, with such an expansion apparatus various disadvantages have been encountered. In particular, the degree of expansion and thus finally the filling power of the tobacco material cannot be adjusted and thus varied.
Also, in the pneumatic transport of the tobacco material falling freely from the rotary vane feeder into the expansion chamber, not all of the tobacco particles come into intensive contact with the hot gas so that a comparatively inhomogenous expansion results, considered along the total volume of tobacco particles to be treated.
Furthermore, due to moisture tobacco particles can deposit in the rotary vane wheel and in the expansion chamber and this can lead to a clogging of the apparatus.
Finally, the known expansion apparatus has a high hot gas, generally steam, consumption so that methods are also being sought for reducing the costs involved.